Coded track circuit railway signaling system



- March 11, 1958 LUFT 2 ,8Z6,685

CODE-D TRACK CIRCUIT RAILWAY SIGNALING SYSTEM "5 Sheets-Sheet 1 Filed Aug. 5, 1954 a; 5% 32 I' Q K 4 N I M t if. z y

' 1NVENT0R., P/zz'lv HLll/. BY WL W- March 11, 1958 P. H. LUFT 2,826,685

CODED TRACK CIRCUIT RAILWAY SIGNALING SYSTEM Filed Aug. 5, 1954 3 Sheets-Sheet 3 E 2411: Y E r F6569! ELI-(BX NX 24m ll Y a" wax 241 514 2.4111! Q 1v N 15 v MM I: W 1 I INVENTOR. Phlg'v HLuf.

H15" ATTORNEY United States Patent CODED TRACK CIRCUIT RAILWAY SIGNALING SYSTEM Philip H. Luft, Penn Township, Allegheny County, Pa, assignor to Westinghouse Air Brake Company, Wil merding, Pa., a corporation of Pennsylvania Application August 5, 1954, Serial No. 447,938

8 Claims. (Cl. 246-34) My invention relates to coded railway signaling systerns, and particularly to an improved arrangement for supplying coded energy in a coded railway signaling system for the control of cab signals and/ or speed control equipment on vehicles traveling through a stretch of track equipped with apparatus embodying my invention.

In conventional coded railway signaling systems, energy coded at one or another of several dilierent rates, say, for example, 180 or 75 times per minute, is supplied to the rails of a section of track at the exit end thereof, and flows over the section rails to apparatus located at the entrance end of the stretch, which apparatus is selectively responsive to the reception of impulses of energy at the various code rates to thereby control wayside signals or other tratrlc controlling devices. Continuous inductive cab signals or automatic speed control for vehicles which travel over the stretch may be provided by employing alternating current energy for the trackway codes, and providing suitable apparatus on the vehicles for detecting the presence of such codes in the track rails of the section over which the vehicle is traveling. Such cab signal apparatus is usually arranged so that the cab signal aspect repeats the aspect of the wayside signal previously passed by the train. That is, when a train passes a signal displaying a green or clear aspect, coded energy at a particular rate, say, for example, 180 times per minute, is being supplied to the rails of the section at the exit end thereof. The reception of code at the 180 code rate by the train-carried apparatus will cause the cab signal apparatus to display a green or clear aspect. If the train passes a signal displaying a yellow or approach aspect, the apparatus is usually arranged so that coded energy at the 75 code rate is supplied to the rails of the section in advance of the signal so that the cab signal apparatus will display a yellow or approach aspect in the cab of the vehicle. The presence of steady energy, the absence of energy, or the presence of energy at a frequency which is ineffective to operate the cab signal apparatus will each cause the cab signal to display a restrictive or caution aspect. It will accordingly be seen that when a train passes a wayside signal displaying an approach aspect with the signal in advance displaying .a red or stop aspect, the cab signal apparatus will continue to display a yellow or approach aspect throughout the entire length of the section.

It is sometimes preferred to provide What is known in the railway signaling art as a code change point at an intermediate point in the track stretch between wayside signals so that energy coded at the 75 code rate may be supplied to the rails of the section from the code change point to the signal in the rear, but steady energy or no energy is supplied to the section in advance of the code change point, that is, the section between the code change point and the signal in advance. Such an arrangement is particularly useful for wayside signals which display an absolute stop aspect, requiring all trains to come to a stop and remain stopped as long as the signal displays its stop aspect. With such an arrangement, if the wayside signal is displaying its stop aspect, the next signal in the rear will display its approach aspect. A train passing the next signal in the rear will receive code energy, and accordingly an approach cab signal aspect will be displayed, until the train passes the code change point, at which time the cab signal will operate to display its restrictive or caution aspect, thus giving additional warning to the engineman that he is approaching an absolute. stop signal. Under such circumstances, the apparatus must be arranged so that, when the signal in question dis,- plays a clear or approach aspect, energy coded at the code rate will be supplied to the rails of the section immediately in the rear of the signal, and will be cascaded at the code change point intermediate in the stretch, so that the section in the rear of the code change point is also supplied with energy coded at the 180 code rate.

However, when the signal in question is at stop, theapparatus must be arranged in such manner that energy at the 75 code rate will be supplied to the rearmost. section of track, that is, the section between the code change point and the next signal in the rear of the signal in question when a train is occupying this first section, and no energy will be supplied to the second section extending between the code change point and the signal in question when a train is occupying this second section.

Although a number of methods have been proposed. in the past for providing such operation and providing;

siutable equipment for use with code change points, suchapparatus usually has the disadvantage. of requiringline wire control circuits extending between the signal locations and the code change point location.

Accordingly, it is an object of my invention to provide an improved coded railway signaling system, arranged:

to provide a code change point location in a section of track extending between two wayside signal locations, with the apparatus arranged so as to require: no line wires between either of the signal locations; and the codechange point location.

Another object of my invention is to provide, an. im.--

back code energy being generated by a novel arrangement.

of apparatus which insures that the feedback code impulses will not interfere with the proper transmission of the master code impulses supplied from the signal location in advance, notwithstanding the fact that the master code energy must be coded at a plurality of different code frequencies in accordance with traffic conditions in ad.- vance of the section.

A further object of my invention is to provide a coded railway signaling system in which, at a code change point, feedback coded energy is supplied to the rails of the sec tion extending between the code change point location and the next signal location in advance, such feedback code energy being generated by a novel arrangement of relay circuits for generating impulses of reverse code energy having a specified time duration and occurring at a specified time during the code cycle, notwithstanding the frequency of the master code energy supplied to the code change point location from the signal location in advance.

Other objects of my invention and features of novelty thereof will become apparent from the ttollowing descrip tion taken in connection with the accompanying drawings.

I shall describe two preferred embodiments of my invention, and shall then point out the novelty in the claims.

In practicing my invention, I provide, in a coded rail:

way signaling system using trackway codes of alternating current having a given frequency for the control of cab signal equipment on trains which move through a section of track, apparatus which transmits reverse code impulses or feedback code impulses from the normal entrance end of the section to the normal exit end of the section. These impulses of reverse code energy are transmitted at a rate less than the frequency of traffic con trolling code impulses supplied from the apparatus at the normal exit end of the section, and the reception of these reverse or feedback code impulses at the exit end of the section governs suitable means for controlling the supply of the master code impulses of track energy to the rails of the section at the exit end thereof.

The reverse code impulses are generated as the result of the recurrent operation of a first and a second impulse relay, which are arranged to govern each other to recurrently operate in a cyclic manner such that the first relay is recurrently picked up for a relatively short time interval, with the off intervals between the picked-up periods being substantially longer than the on or picked-up periods. This first impulse relay is employed to govern the supply of energy to the track rails at the normal entrance end of the track section.

When no master code energy is being received at the entrance end of the section, the two impulse relays operate recurrently at a rate determined by their parameters and the parameters of their controlling circuits. However, when impulses of master code energy are being received at the entrance end of the section, the first impulse relay is additionally governed by the code following track relay which is operated by the master code impulses, to thereby obtain proper synchronization of the master and reverse code impulses.

In the drawings, Figs. 1A and 1B, when placed side by side with Fig. 113 to the right of Fig. 1A, illustrate in a diagrammatic manner a stretch of railway track equipped with a signaling system embodying my invention, and

,Fig. 2 is a fragmentary diagrammatic view of a modification of the apparatus shown in Fig. 1A.

Referring to Figs. 1A and 1B of the drawings, there is shown a stretch of railway track including track rails 3 and 5, extending between two wayside signal locations 28 and 4S, and divided into a first track section designated by the reference character 2T, a second track section designated by the reference character ZAT, and a third track section in advance of signal 48 designated by the reference character 4T by the usual insulated rail joints 7. The wayside signals 23 and 4S govern the movements of trafiic through the sections in advance of the signals, signal 28 governing the movement of tralfic into the stretch including sections ET and ZAT, and signal 48 governing the movement of traffic into section 4T. The signals may be of any of the well-known types, and as here shown, are of the color light type of signal having a green lamp G which when lighted provides a clear aspect, a yellow lamp Y which when lighted provides an approach aspect, and a red lamp R which when lighted provides a stop aspect.

As indicated by the arrows on the drawings, trafiic normally moves through the stretch of track including sections 2T, 2AT and 4T in the direction from left to right, and it is assumed that vehicles or trains moving through the section are equipped with cab signal or train control apparatus of the type well known in the art which responds to the presence of alternating current energy of a predetermined frequency supplied at different code rates to the section rails, through the medium of inductive pickup apparatus on the vehicle or train. A detailed description of the vehicle-carried apparatus is not included herein since this apparatus may be any one of a number of suitable types, and may be, for example, of the type shown and described in Letters Patent of the United States No. 2,462,454, issued to Leslie R. Allison on February 22,

4 1949, for Train-Carried Cab Signal Apparatus. It is deemed sufficient to point out that the apparatus on the vehicles or trains which move through the stretch of track is arranged so that alternating current energy having a frequency of 190 cycles and supplied to the rails of the section at the rate of 180 times per minute will cause the display of a clear aspect on the cab signal apparatus, whereas the presence of 100 cycle energy in the section rails coded at the code rate will cause the display of an approach aspect on the cab signal apparatus, and the presence of steady energy having a 10-0 cycle carrier fre quency, or the absence of any energy, or the presence of cycle energy at code rates less than 75 impulses per minute will cause the apparatus to display a restrictive aspect in the cab of the vehicle or train. It is also to be pointed out that the vehicle-carried apparatus will not respend to any coded energy other than that having the 100 cycle carrier frequency.

The apparatus located at the first signal location, that is, the location of signal 28, includes a code following track relay ZTR connected across the rails of section MT through a 100 cycle filter, which filter is constructed and arranged in the usual manner so that only alternating current energy having a frequency of 100 cycles per second will be supplied therethrough to operate the relay ZTR. For detecting the code following operation of relay ZTR, there is provided a decoding transformer ZDT, which governs the operation of a signal control relay ZHR, and also governs a clear signal control relay ZDR through a decoding unit ltltlDU, the relays ZHR and 2BR governing the aspect displayed by the Wayside signal 25. At the code change point, located at a point intermediate in the stretch and at the point of adjacency of the track sections 2T and ZAT, there is provided a track transformer ZTT having a secondary winding connected across the section rails and having a primary winding supplied with energy by a circuit including a contact of the code following track relay ZATR which is arranged to be connected at times to the rails of section ZAT through a 190 cycle filter, and a back contact repeater relay ZABSA, which is governed by a back contact of the track relay ZATR. The apparatus at the code change point location also includes a reverse code track transformer ZAITI which is energized in a manner to be subsequently described for supplying impulses of energy to the rails of section EAT at the lefthand or entrance end thereof, under the control of a first impulse relay ZAIR, which in turn is governed in part by a second impulse relay ZAl'M. The apparatus further includes a code following track relay repeater relay ZATM, and a front contact repeater relay ZAFSA, plus a snubbing circuit including a capacitor Q1 and a resistor R1 for at times rendering relay ZAIR slightly slow in releasing.

At the second signal location, Fig. 13, there is provided a track transformer ZATT, arranged so that energy may be supplied at times through this transformer to the rails of section ZAT at the exit end thereof, an approach code following relay 4AR which is arranged to be connected at times across the rails of section ZAT through a 100 cycle filter, and a slow release code detecting approach repeater relay 4AM, which is arranged to be ener: gized by code following operation of relay 4AR, utilizing a snubbing circuit comprising a capacitor Q2 and a resistor R2. The apparatus at the signal location 45 also includes a code transmitting relay 4CTM, which governs the supply of master code impulses to the rails of section S ZAT at the exit end thereof, this code transmitting relay being supplied with impulses of energy from code transmitting devices designated by the reference character CT preceded by a number indicating the frequency of their operation, namely, ISQCT and '7 5C1", which operate their contacts respectively at the rates of and 75 times per minute. The selection of the code operating speed for the code transmitting relay dCTM is provided by contacts of relays 4HR and lDR, the controls of which are not shown,

but which are governed by traffic conditions in advance of v signal 48 in any suitable manner, as, for example,'in a manner similar to that shown for relaysZHR and 2BR associated with signal 28. The contacts of relays 4HR and 4DR also govern the lighting circuits for signal 48 in a conventional manner.

Energy for the operation of various of the relays is furnished by a suitable source of low voltage direct current, not shown, and having positive and negative terminals designated by the reference characters 3 and N, respectively. It is to be understood that such a source is provided at each of the three locations shown on the drawings. The 100 cycle energy supplied for the operation of the coded track circuits in the cab signal equipment on trains moving through the stretch is supplied from a suitable source of alternating current energy, not shown, but having terminals designated by the reference characters BX and NX, and it is to be understood that such energy may be fur nished through the medium of a suitable transmission line extending along the stretch of track.

The contacts of relays which are recurrently operated are designated by dotted lines showing the alternative positions of the contacts, and the contacts of relays which are slow in operating are designated by arrows therethrough pointing in the direction in which the relay is slow to operate, i. e., downwardly for slow releasing relays and upwardly for slow pickup relays.

It is believed that a better understanding of my invention may be had by a detailed analysis of the operation of the arrangement shown in the drawings under various traffic conditions. The operation of the apparatus shown in Figs. 1A and IE will be described first.

The apparatus is shown in the condition which it assumes when trafiic conditions in advance of signal 43 are such that the signal control relays 4HR and 4DR: at signal location 48, Fig. 1B, are released. With relay dHR released, an obvious circuit including back contact c of relay 4HR supplies energy to the red lamp R of signal 48 so that this signal displays a stop aspect.

For the purposes of a preliminary general description, it will be assumed that reverse code impulses generated by the apparatus at the code change point location are being supplied to the track rails 3 and 5 of section ZAT at this time at the entrance end thereof, and are being supplied to the winding of relay iAR through the 100 cycle filter, during each released period of the code transmitting relay 4CTM, the back contact b of relay 4CTM closing the circuit for energizing relay 4AR. The recurrent operation of the contacts of relay 4AR causes energy to be supplied to the winding of relay 4AM, since each time that contact a of relay 4AR is picked up, energy is supplied by an obvious circuit to the capacitor Q2 through the limiting resistor 42, and when contact a of relay 4AR is released, the energy stored in capacitor Q2 is supplied through the winding of relay 4AM. Relay 4AM is selected and arranged in such manner that its release period is longer than the longest off time of the reverse code impulses which operate relay 4AR, so that the contacts of relay 4AM remain picked up during the intervals in which no energy is being supplied to its winding. With contact a of relay 4AM picked up, a circuit is established for supplying energy from the 75 code transmitter to the winding of relay 4CTM each time that contact b of relay 4AR is released. This circuit may be traced from terminal B at front contact a of the code transmitter 750T, over front contact a of relay 4AM, back contact b of relay 4AR, back contact a of relay 4BR, and through the winding of relay 4CTM to terminal N. Aspreviously pointed out, the impulses of reverse code energy are of very short duration, and Occur at a rate much lower than the 75 code rate, so that during the intervals which the impulses of energy are not received, contact b of relay 4AR will be released to complete the circuit traced above, so that the' winding of relay 4CTM leased. Accordingly, it will be seen that, at this time is energized by energy supplies over the contacts of 1 the reference characters BX and NX to the primary winding of the track transformer ZATT. These impulses of master code energy, governed by the operation of relay 4CTM, are supplied to the rails 3 and. 5 of section 2AT, through the 100 cycle filter, which presents only a low impedance to the 100 cycle energy, so that the larger portion of the energy is supplied to the track rails of the section in the usual manner.

The impulses of master code energy supplied from the exit end of section ZAT at the code rate flow over the section rails to the code change point location shown in Fig. 1A, and through the secondary winding of transformer ZAITT and the cycle filter to the winding of relay ZATR. The circuit for energizing relay ZATR is governed by a back contact b of the impulse relay ZAIR in multiple with the front contact of relay ZATR. It will be assumed for the purposes of this preliminary discussion that contact b of relay 2AIR is released at the time that the 75 code impulse of master code energy is supplied to the rails of the section and, accordingly, energy is supplied through the 100 cycle filter to the winding of relay ZATR. When contact aof relay ZATR picks up, it establishes a stick circuit for itself to insure that energy will continue to be supplied to the winding of the relay, even in the event that contact b of relay ZAIR subsequently picks up before the impulse of master code energy is interrupted. The recurrent supply of impulses of energy to the winding of relay ZATR causes its contacts to be operated at the corresponding code rate of 75 times per minute, so that relay ZABSA is recurrently energized. by a circuit including back contact d of relay ZATR. The relay ZABSA is selected and arranged so that its contacts are slower in releasing than the maximum picked-up time of relay ZATR, so that as a result relay ZABSA will be picked up as long as relay ZATR is being supplied with coded energy at either one of the two code rates. With contact a of relay ZABSA picked up, each time that contact 0 of relay ZATR picks up, a circuit is established for supplying energy to the primary winding of transformer ZTT, which circuit includes front contact c of relay 2ATR, front contact a of relay ZABSA, and the primary winding of transformer 2TT. Accordingly, impulses of energy coded :at the 75 code rate will be supplied to the rails of section 2T at the exit end thereof and will flow over the section rails to the entrance end through the 100 cycle filter to operate the contacts of relay 21' R. ZTR causes the supply of energy to the top and bottom sections of the primary winding of decoding transformer 2DT with the consequent induction of alternating current energy having a frequency the same as the operattion of the contacts of relay ZTR in the secondary winding of the decoding transformer. This alternating current energy is mechanically rectified bythe simultaneous and synchronous operation of contact b of relay ZTR, and is supplied to the winding of the signal control relay ZHR. This results in the energization of relay ZHR, which has its contacts picked up as long as the track relay ZTR is following code at either one of the. two master code rates. Energy is also supplied from the autotransformer portion of the decoding transformer ZDT to the decoding unit DU, to supply energy to the winding of relay ZDR. The parts are arranged in the manner well known in the art so that sufiicient en- 'ergy to pick up the contacts of relay ZDR is supplied to the winding of the relay when and only when the contacts of relay ZDR are operating at the 180 code rate, and at other times, the contacts of relay ZDR are re- The recurrent operation of contact a of relay ZHR is picked up, thereby establishing an obvious circuit'for supplying energy to the yellow lamp Y of signal 28, so that signal 28 displays an approach aspect.

When signal 48, Fig. 1B, is displaying a yellow or an approach aspect, as determined by the energized condition of relay ll-IR and the energized or deenergized condition of relay 4BR in accordance with traffic conditions in advance of signal 45, contact a of relay 4HR will be picked up to connect the winding of relay eCTM to the circuit including front contact a of code transmitter ISiPCT, so that the contacts of relay 4CTM are operated at the 180 code rate at this time. Accordingly, the supply of energy to track section EAT at the exit end thereof is coded at the 180 code rate, causing the corresponding rate of operation of relay ZATR at the code change point location, Fig. 1A. The recurrent operation of contact c of relay ZATR at the 180 code rate will cause a supply of impulses of alternating current energy at the same rate to the rails of section 2T at the exit end thereof, and as a result, relay ZTR at the entering end of section 2T will operate its contacts at the 180 code rate, so that the contacts of both relays ZHR and 29?. will be picked up, thereby establishing a circuit for supplying energy to the green lamp G of signal 25. If the supply of 100 cycle energy to the filter and thence to the winding of relay ZTR at the entrance end of section 2T is cut off for any reason, such as by the occupancy of section 2T or section 2A1 by a train, the contacts of relay ZTR will cease operating, with the result that relays ZHR and ZDR will release, the contact b of relay ZHR establishing a circuit for supplying energy to the red lamp R of signal 25, so that the signal thereby displays a stop aspect.

As previously pointed out, when signal eS'is displaying a red or stop aspect, signal 25 will display a yellow or approach aspect, and the energy supplied to the rails of sections 2T and ZAT will be coded at the "'5 code rate. If a train moving from left to right passes signal 28, the shunting effect of the wheels and axles of the train will cut ofr the supply of energy to the winding of relay ZTR, so that relays ZHR and will be released with the consequence that signal 23 will display a stop aspect behind the train. The impulses of energy at the 75 code rate supplied at the exit end of section 2T will cause the cab signal apparatus on the train to display a yellow or approach aspect on the cab signal. As the train moves into section ZAT, the supply of impulses of reverse code energy from the entering end of section ZAT at the code change point location to the exit end of section 2AT, Fig. IE, will be cut oil. Accordingly, the winding of approach relay 4AR will no longer be energized by the impulses of reverse code energy during periodic ofl? intervals of the master code energy supplied at that end of the section, and contacts a and I) of relay 4AR will release and remain released. After a short time interval, the contact a of relay 4AM will release, since energy is no longer being recurrently supplied to the winding of this relay over contact a of relay 4AR, and the opening of front contact a of relay 4AM will interrupt the circuit for supplying energy to the winding of the code transmitting relay iC'lM. With relay 4CTM deenergized, the supply of impulses of 75 code to the rails of section EAT will be interrupted so that the cab signal apparatus on the approaching train will change the aspect displayed by the cab signal from approach to restricting, thereby indicating to the engincman that he is approaching a stop signal.

If it is then assumed that the traific conditions in advance of signal 48 become such that signal changes its aspect from stop to approach or clear, the train in section ZAT will then have the aspect of the cab signal thereon changed, since relay ll-IR will be picked up upon the clearing of signal 48, so that the winding of code transmitter 4CTM will be connected to the source of energy over contact a of the code transmitter ldilCT, with the result that 100 cycle energy coded at the rate of 180 times per minute will be supplied to the rails of section 2AT and thereby operate the cab signal apparatus on the train in section ZAT to provide a clear aspect.

When the train in question passes signal 45 and enters section 4T, relay ll-IR will be released, and its contact a will interrupt the circuit for supplying energy to the winding of the code transmitting relay dCTM, so that the supply of cycle energy to the rails of section 2AT will again be cut off.

While the train is occupying section 2AT, impulses of reverse or feed-back code energy are supplied from the code change point location by the operation of the equipment in a manner to be subsequently described. These impulses of reverse code energy are supplied over the rails of section ZAT behind the train as it proceeds through section ZAT, and when the rear of the train vacates this section, these impulses will cause the recurrent operation of relay 4AR, so that the code detecting relay 4AM will again be energized. With relay 4AM energized, the circuit previously traced for energizing relay 4CTM over front contact a of the code transmitter 75CT is again established, and impulses of master code energy are accordingly transmitted from the exit end of section ZAT to the entrance end thereof; Relay ZATR is accordingly operated at the corresponding rate, to thereby cause the supply of coded energy at the 75 code rate to the exit end of section 2T, which energy feeds over the section rails to the entrance end of this section, and causes operation of the contacts of relay ZTR at the 75 code rate. As a result, relay ZZl-IR will be picked up, and with relay 2BR released, the circuit for supplying energy to the yellow lamp Y of signal 28 is again established.

If the signal 48 is displaying a yellow or green aspect, the energy supplied to the sections 2AT and 2T will be coded at the code rate, so that signal 28 will display its clear or green aspect, and if a train enters section 2T at this time, the cab signal apparatus on the train will be energized by impulses of energy at the 180 code rate so that the cab signal will display a clear aspect. When the train enters section ZAT, the reverse code impulses supplied from the code change point location and fed over the section rails toward the exit end of the section will be shunted by the train, but this will have no effect on the transmission of master code from the exit end of the section, since contact a of relay 4HR will be picked up to thereby govern the operation of the code transmitting relay 4CTM directly over contact a of the code transmitter 180CT. Although relay 4AR will cease its operation upon the entrance of the train in section ZAT, due to the shunting of the reverse code impulses, relay 4AM will remain picked up at this time, since an auxiliary energizing circuit is closed over front contact b of relay 4HR. This auxiliary energizing circuit is provided to maintain the relay 4AM energized under the condition in which signal 43 has its aspect changed from clear or approach to stop, in which case a lapse of time occurs before the reverse code impulses supplied to relay 4AR are effective to energize the relay 4AM.

Having thus described in a general manner the mode of operation of the coded railway signaling system shown in the drawings, I will now describe in detail the operation of the apparatus at the code change point location which is effective to generate impulses of reverse code energy for energizing the approach relay at the exit end of section ZAT.

As previously pointed out, the pickup circuit for relay ZATR includes a back contact b of the impulse relay ZAIR, and a stick circuit is provided for relay ZATR including front contact a of relay ZATR, so that the release of the impulse relay ZAIR is checked over its back contact b before relay ZATR can be picked up, but, thereafter, relay ZATR will remain picked up for the duration of a master code impulse, by virtue of the stick circuit established over its own front contact a. The.v

transformer ZAITT has its primary winding controlled by a circuit including contact b of relay ZATR and contact a of relay ZAIR. As will be seen from the drawings, the primary winding of transformer ZAITT is shortcircuited when contact a of relay ZAIR is released, or when contact b of relay ZATR is picked up. Under either of these circumstances, the primary winding of transformer ZAITT is short-circuited in order to provide a low impedance path through the secondary winding for supplying energy to the Winding of relay ZATR. Energy is supplied from the alternating current source to. the primary winding of transformer ZAI TT during the time that contact b of relay ZATR is released and contact a of relay ZAlR is picked up. Accordingly, it will be seen that if relay ZAlR is picked up at the time that contact b of relay ZATR releases, energy will be supplied to the rails of section ZAT through the transformer ZAITT, to thereby supply an impulse of reverse code energy to the apparatus at the exit end of section ZAT.

The first impulse relay ZAIR and the second impulse relay ZAIM are controlled in such manner that these relays operate in a predetermined cycle to result in the periodic operation of relay ZAIR to produce code impulses having a relatively short on time and a relatively long oil time, with the relays being governed by the action of track relay ZATR in such manner that at times relays ZAIR andl ZAIM function as a pulse generating circuit which can operate independently of the operation of relay ZATR, and at other times operate as a pulse 9 generating circuit which is synchronized with the operation of relay ZATR.

Considering the first instance, let it be assumed that no impulse of master code energy are being supplied through the secondary winding of transformer ZATT and the 100 cycle filter to the winding of relay 2ATR, which condition may be the result of a train occupying section 2AT. Under these conditions, it will be remembered that the apparatus at the code change point location continues to generate impulses of reverse code energy, so that when the train vacates section ZAT, the reverse code impulses will cause the operation of the approach relay 4AR and the subsequent energization of the detector relay 4AM at the exit end of section 2AT, to thereby restore the master code energy governed by the 75 code transmitter at that location. Under such circumstances, at the code change point location, relay ZATR will have its contacts continuously released. Accordingly, no energy will be supplied to the winding of relay ZATM, since the circuit for energizing this relay is open at front contact (I of relay ZATR. With relay ZATM deenergized, the circuit for supplying recurrent impulses of energy to the winding of relay ZAFSA will be interrupted at front contact a of relay ZATM, so that relay ZAFSA will also be released at this time.

Assuming that contact c of relay ZAIR is released, energy is supplied by an obvious circuit to the Winding of relay ZAIM. Relay ZAIM is a relay characterized by being relatively slow in picking up its contacts after its winding has been energized. Accordingly, after a predetermined time interval iollowing the release of the contacts of relay ZAIR, the contacts of relay 2AIM will pick up. When contact a of relay ZAIM picks up, energy is supplied to the winding of relay ZAIR over a circuit including back contact a of relay ZAFSA and the winding of relay ZAIR to terminal N. Additionally, the capacitor Q1 is charged through the resistor R1. When relay ZAIR picks up, the circuit for supplying energy to relay ZAIM is interrupted at back contact c of relay ZAIR, and relay ZAIM thereafter releases. The release of contact a of relay ZAIM interrupts the circuit for energizing relay ZAIR, but the energy stored. in the capacitor Q1 is then supplied over back contact a of relay ZAFSA and through thewinding of relay ZAIR, so that relay ZAIR is maintained in its energized condition for a short time interval. After the expiration of this time interval,-

relay ZAIR will release, and its back contact c will again close the energizing circuit for relay ZAIM, whereupon relay ZAIM again picked up, reener-gizing relay ZAIR. It will be seen, therefore, that at this time, with relay ZATR continuously deenergized, the relays ZAIR and ZAlM will successively pick up and release. The relays are selected and arranged and the capacitor Q1 and resistor R1 are proportioned so that the cycle of operation of relay 2AlR is represented by a relatively short time in which the contacts of relay 2AIR are picked up, followed by a relatively long interval during which the contacts of relay ZAIR are released. These time intervals may be, for example, of the order of 0.08 second to 0.130 second for the on or picked-up time of relay ZAIR, and an o or released time for relay ZAIR of the order of 1.5 seconds.

With contact b of relay ZATR released, energy is supplied to the primary winding of transformer ZAITT each time that contact a of relay ZAIR picks up, with the result that impulses of energy having a relatively short on time and a relatively long off time are supplied to the rails of section 2-AT.

When section 2AT is unoccupied, the impulses of reverse code energy supplied from the apparatus at the code change point location operate the code following approach relay 4AR at the exit end of section 2AT, the cycle of operation of this relay following; that of the reverse code energy in that its contacts are released for a relatively long period and picked up for a relatively short period. If the signal 48 is at stop, so that back contact a of relay 4HR is closed, the code transmitting relay 4CTM is operated recurrently at the code. rate during the long off periods of the reverse code energy in which contact b of relay 4AR is released to complete the circuit for governing relay 4CTM. When an impulse of reverse code energy picks up relay 4AR during the released time of contact b of relay 4CTM, the circuit for governing relay 4CTM is momentarily opened at back contact b of relay 4AR, and when the impulse of reverse code energy ceases, contact b of relay 4AR is again closed, so that relay 4CTM can again operate to code the supply of energy from transformer 2ATT to the section rails. Accordingly, it will be seen that, during the unoccupied condition of section ZAT with signal 48 at stop, the master code energy supplied from the exit end of the section to the entrance end of the section consists of master code impulses at the 75 code rate, interspersed at intervals by an impulse of reverse code energy.

The operation of relays ZAIR and ZAIM under the condition in which track relay ZATR is operating in response to impulses of master code energy supplied from the exit end of section ZAT is substantially similar to the operation of the relays when the track relay ZATR is continuously released. However, as previously pointed out, the operation of the impulse generating relays may be synchronized with the operation of the track relay ZATR, so that the reverse code impulses are transmitted at the proper time and so that there is no interference with the reception of the master code impulses. With relay ZATR operating its contacts, relay ZAFSA will be picked up, and relay ZAIR is then governed by a pickup circuit which includes front contact a of relay ZAFSA, back contact 11 of relay ZATM, front contact b of relay ZAIM, and front contact d of track relay ZATR. A stick circuit is. provided for relay ZAIR including front contact c of relay ZAIR, front contact b of relay ZATM, and front contact a of relay ZAFSA. It will be seen that relay ZAIR cannot pick up immediately if relay ZAIM picks up during the time that the track relay ZATR is picked up because the pickup circuit for relay ZAIR is interrupted at back contact b of relay ZATM, which will be picked up while the contacts of relay 2ATR are picked up. In: this manner, the energization of: relay ZAIR cannot take place during the very short ll interval when the contact d of relay ZATR happens to pick up after contact b of relay ZAIM picks up, so that insurance is provided that relay ZAIR will always be picked up for a minimum time interval which is sufliciently long to insure the proper operation of the apparatus to transmit a reverse code pulse of sufiicient duration to properly operate the apparatus at the exit end of section 2AT.

However, on the next pickup of relay ZATR, relay ZAIM will still be picked up, and a pickup circuit will be established over front contact d of relay ZATR, front contact 11 of relay ZAIM, back contact b of relay ZATM, front contact a of relay ZAFSA, and through the winding of relay 2AIR to terminal N. The relays are selected and designed so that the time required for relay ZAIR to pick up following the pickup of relay ZATR is much less than the time required for relay ZATM to pick up. Ac cordingly, relay 2AIR will pick up, followed by the picking up of relay ZATM. When contact I; of relay ZATM picks up, it interrupts the pickup circuit just traced for relay ZAIR, but establishes the stick circuit for the relay which includes front contact [1 of relay ZATM and front contact of relay ZAIR. Accordingly, relay ZAIR will remain picked up until relay ZATM releases following the release of contact b of relay ZATR. As pointed out hereinbefore, the release of contact b of relay ZATR, with contact a of relay ZAIR picked up, will result in energy being supplied to the winding of transformer ZATT, so that an impulse of reverse code energy is supplied to the rails of section ZAT. Shortly thereafter, relay ZAIR will release, and its contact 0 will interrupt the stick circuit for relay 2AIR and reestablish the energizing circuit for relay ZAIM, which after a relatively long time interval will pick up its contacts, so that the cycle described above will be repeated.

The apparatus is constructed and arranged in such manner, and the operating times of the various relays are so chosen, that the apparatus functions to transmit a pulse of reverse code energy during at least every second or third cycle of the master code energy impulses. The frequency at which'the impulses of reverse code energy are transmitted from the entrance end of section 2AT is sufiiciently low that the cab signal apparatus on a train which may under certain circumstances be moving through the section in the direction opposite to that of normal traffic, namely, from right to left rather than from left to right, will not be affected, since the frequency at which the impulses would be received by this equipment is too low to cause operation of the cab signal apparatus.

As previously is energized as a result of the recurrent operation of contact a of relay 4AR when reverse code energy is being received at the exit end of section ZAT. An auxiliary energizing circuit governed by front contact b of relay 4HR also supplies energy to the winding of relay 4AM as long as relay 4HR is picked up, so that signal 45 is displaying a yellow or green aspect. When signal 48 changes its aspect to stop by the release of relay ti-IR, the intervening interval in which the contacts of relay 4AR will not be operating might be sutficiently long to cause relay 4AM to release, with the result that its contact a would interrupt the circuit for governing the code transmitting relay 4CTM. Accordingly, the auxiliary energizing circuit will provide energy to charge the capacitor Q2, so that at the time that relay {tHR releases, with contact a of relay 4AR released, relay 4AM will remain in its picked-up position for a sufficiently long time interval to permit the initiation of the transmission of reverse code impulses from the entrance end of section 2A1, to thereby maintain relay 4AM picked up.

Referring now to Fig. 2, there is shown a fragmentary diagram illustrating the apparatus employed at the code change point location in a' second embodiment 'of my invention, which employs one less relay than the arrangement shown in Fig. 1A. The principal difference be.-

pointed out, the relay 4AM, Fig. 1B,

' transmission of an impulse of reverse code energy after the track relay ZATR has been released for an interval sufiiciently long to allow the reverse code impulse relay to pick up. In other words, the impulses of reverse code energy are delayed in their transmission by the amount of time required for the impulse relay ZAIR to pick up after the release of the track relay ZATR, whereas in Fig. 1A, the impulse of reverse code energy was transmitted immediately upon the release of the contacts of the track relay ZATR, since the reverse code impulse relay 2AIR was picked up prior to the release of the track relay ZATR.

With the arrangement shown in Fig. 2, the track repeater relay ZATM is not required, but the arrangement shown in Fig. 2 is limited to operation with track circuits in which the parameters are such that the increase in time required for the transmission of the reverse code impulse will not limit the proper operation of the apparatus.

In describing the operation of the apparatus shown in Fig. 2, it will first be assumed that no code energy is being received from the exit end of section 2AT, and that the apparatus at the code change point location is functioning to generate impulses of reverse code energy having a duration and repetition frequency determined by the constants of the relays and associated apparatus.

With the contacts of relay ZATR continuously released, relay ZAFSA will be released, since no energy is supplied thereto by the circuit including front contact I) of relay ZATR. With relay ZAIR released, an energizing circuit for the slow pickup relay ZAIM is established over back contact c of relay ZAIR, and after a time interval determined by the pickup characteristics of relay ZAIM, this relay will pick up its contacts. When contact a of relay ZAIM closes, a shunt circuit around the winding of relay ZAIM is established, including the current limiting resistor R4. It will be apparent that this circuit has no effect upon the pickup time of relay ZAIM, but does serve to provide a snubbing circuit for. delaying the release of relay ZAlM.

When contact 0 of relay ZAIM picks up, a circuit is established for supplying energy to the winding of relay ZAIR, which circuit may be traced from terminal B at back contact a of relay ZAFSA, over back contact 0 of track relay ZATR, front contact 0 of relay ZAIM, and through the winding of relay ZAIR to terminal N. When relay ZAIR picks up, its front contact a establishes an obvious circuit for supplying cycle energy to the primary winding of the impulse transformer ZAITT, so that the track section ZAT is supplied with 100 cycle energy at the entrance end thereof. When contact 0 of relay ZAIR picks up, the circuit for energizing relay ZAIM is interrupted and after a short time interval the contacts of relay ZAIM will release. The opening of front contact c of relay 2AIM interrupts the previously traced, circuit for energizing relay ZAIR, but this relay is slightly slow in releasing, and its contacts will remain picked up until the contacts of relay ZAIM have closed their back contacts. When back contact 0 of relay ZAIM closes, the winding of relay ZAIR is directly shuInted thereby, further delaying the release of relay 2A R.

When relay ZAIR finally releases its contacts, its contact a interrupts the circuit for supplying energy to the winding of transformer ZAITT, thereby terminating the impulse of reverse code energy, and its back contact 0 reest'ablishes the circuit for energizing the winding of relay ZAIM, so that the cycle described above is repeated. The circuit components and the relays are con structed and arranged in such manner that the impulses of reverse code energy are supplied with a relatively short 13 on time and arelatively long olf time as previously described in connection with Fig. 1A.

Under the condition in which master code energy is being received at the entrance end of section 2AT, causing the code following operation of track relay 2ATR, the apparatus for generating the reverse code impulses, must of course, be properly synchronized so that the impulses of reverse code energy are transmitted at the proper times so as not to interfere with the reception of the master code impulses. This operation is different under different circumstances, depending upon the operation of the track relay ZATR, and, accordingly, the detailed operation of the apparatus under these different conditions will now be described.

It relay ZAIM picks up its contacts during the time that track relay ZATR is released, it is necessary to prevent the picking up of relay ZAIR until after the next on period of relay ZATR, that is, the next time in which the contacts of relay ZATR are picked up. This is necessary since if relay 2AIM picked up just before the termination of the o period of the master code impulse, and relay ZAIR picked up to transmit a reverse pulse, the succeeding pulse of master code energy would be interfered with by the pulse of reverse code energy, thus causing a condition of scrambled code in the track circuit. Referring to the drawing, it will be seen that at this time with the contacts of relay ZATR in continuous operation, energy will be recurrently supplied to the winding of relay ZAFSA each time that contact b of relay ZATR is picked up. Since relay ZAFSA is sufficiently slow in releasing to bridge the periods in which contact b of relay ZATR is released, relay ZAFSA will be picked up at this time. A charging circuit for capacitor Q3 is established each time that contact c of relay ZATR is picked up, provided that contact b of relay ZAlM is also picked up. This circuit may betraced from terminal B at front contact of relay ZATR, over front contact a of relay ZAFSA, front contact b of relay ZAIM, and through the current limiting resistor R3 to the capacitor Q3, the other side of the capacitor being connected to terminal N. When contact b of relay ZAIM is released, it establishes an obvious short-circuiting circuit for the capacitor Q3, so that the capacitor Q3 will be discharged when relay ZAIM is. released. The energy stored by capacitor Q3 can be supplied to the winding of the impulse relay ZAIR by a circuit which includes the limiting resistor R3, front contact 5 of relay ZAIM, front contact a of relay ZAFSA, back contact 0 of relay ZATR, and front contact 6 of relay ZAIM. It can thus be seen that if relay ZAIM picks up with relay ZATR released, no charging energy will be supplied to the impulse relay ZAIR upon the subsequent release of the trackrelay ZATR, since it is necessary that contact 0 of relay ZATR be picked up at the time relay ZAIM is picked up in order to supply energy to the capacitor Q3, and thus if relay ZAIM was not picked up during the previous picked-up time of relay ZATR, no energy will be stored in the capacitor Q3. However, during the next picked-up interval of relay ZA'IR, with relay ZAIM picked up, energy will be supplied to the capacitor Q3, and when relay ZATR releases, the circuit previously traced will be established for supplying energy from the capacitor Q3 to the winding of relay ZAIR, with the result that relay ZAIR will pick up to thereby 'cause the transmission of an impulse of reverse code energy. The picking up of contact c of relay 2AIR will interrupt the circuit for supplying energy to the'winding'of relay ZAIM, but the snubbing circ uit including the resistor R4 is connected across the winding of relay ZAIM at this time by front contact a of relay ZAIM, so that the relay is slowed in its release. Whom relay ZAIM does release, the capacitor Q3 is short-circuited throughthe resistor R3, and additionally, a shorti circuit is established across the winding of relay ZAIRiby back contact 0 of relay. ZAIM so that relay 2AIRis slowed in its releasing for a suflicient time inter'. val to causethe transmission of proper length of reverse code impulse.

If relay 2AIM picks up while relay ZATR is picked up, the circuit for supplying energy from the low voltage source to the capacitor Q3 will be established and when contact c of relay ZATR releases, relay ZAIR will be picked up by the circuit previously traced, to thereby transmit an impulse of reverse code energy. The principal purpose of the resistance snub R4 which is connected across the winding of relay ZAIM when contact a of this relay is picked up is to provide a suflicient release interval on relay ZAIM so that in the event relay ZAIM picks up just before relay ZATR releases, the capacitor Q3 will supply sufiicient energy through the circuit including front contact b of relay ZAIM to insure that relay ZAI R will pick up for a sufficient time interval to send an impulse of reverse code energy of proper length. If the capacitor Q3 has been insufficiently charged due to the fact that relay ZAIM picked up just momentarily before contact 0 of relay ZATR released, capacitor Q3 will not be supplied with sufficient energy to pick up relay ZAIR fully and keep this relay picked up for a sufiicient time duration for sending the reverse code impulse. However, if relay ZAIR is energized sufficiently to cause contact 0 of relay 2AIR to just open, it will be seen that the energizing circuit for relay ZAIM is opened. If the resistance snub for relay ZAIM were not provided, this relay would release, thus requiring relay ZAIM to pick up again before an impulse of reverse code energy could be transmitted. However, with the resistance snub on relay ZAIM, the release of this relay is delayed by a sufficient time interval so that, upon the next energization of relay ZATR, capacitor Q3 will be fully charged, and when contact c of relay ZATR releases, the energy stored in capacitor Q3 will be supplied to the winding of relay ZAIR to thereby pick up this relay and cause the transmission of an impulse of reverse code energy of proper length.

It can be seen from the foregoing that my invention provides a number of useful advantages in that it uses apparatus which is conventional in the railway signaling art, provides the necessary functions for a code change point without the use of line wires, and is noninterfering with the normal operation of the coded track circuit apparatus, so that it may be employed with existing coded railway signaling systems with a minimum of changes in the existing apparatus.

Although I have herein shown and described only two forms of coded railway signaling systems embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with a section of railway track through which trains normally move in a given direction, the trains traversing said section being equipped with cab signal apparatus responsive only to alternating current energy coded at one or another of a plurality of trafiic code rates and being non-responsive to alternating current energy coded at a rate less than the lowest rate of said traffic code rates, the combination comprising supply means at the exit end of said section for at times supplying alternating current energy to the rails of said section at one or another of said trafiic code rates in accordance with trafiic conditions in advance of said section, means at the entrance end of said section for supplying reverse code impulses of alternating current energy to the rails of said section at a rate less than the lowest of said traflic code rates, and detector means at the exit end. of said section responsive only to said reverse code impulses, said supply means being governed by said detector means to cut off the supply of alternating current energy at the exit end of 15 a said section when said reverse code pulses are cut oif and the section next in advance is occupied.

2. In combination with a section of railway track through which trains normally move in a given direction, the trains traversing said section being equipped with cab signal apparatus responsive only to alternating current energy coded at one or "another of a plurality of traffic code rates and being nonresponsive to alternating current energy coded at a rate less than the lowest rate of said traflic code rates, the combination comprising supply means at the exit end of said section for at times supplying alternating current energy to the rails of said section at one or another of said trafiic code rates in accordance with traffic conditions in advance of said section, reverse code generating means at the entrance end of said section for supplying reverse code impulses of alternating current energy to the rails of said section at a rate less than the lowest of said traffic code rates, means associated with said reverse code generating means for synchronizing the transmission of said reverse code impulses with the intervals between the impulses of traflic code energy received from the exit end of said section, detector means at the exit end of said section responsive only to said reverse code impulses, said supply means being governed by said detector means to cut olf the supply of alternating current energy at the exit end of said section when said reverse code pulses are cut olf and the section next in advance is occupied.

3. In combination with a section of railway track through which trains normally move in a given direction, the trains traversing said section being equipped with cab signal apparatus responsive only to alternating current energy coded at one or another of a plurality of different trafiic code rates and being nonresponsive to alternating current energy coded at a rate less than the lowest of said tratfic code rates, the combination comprising supply means at the exit end of said section for at times supplying alternating current energy to the rails of said section at one or another of said traific code rates in accordance with trafiic conditions in advance of said section, code following track relay means located at the entrance end of said section and responsive to alternating current energy supplied thereto over the rails of said section from the exit end of the section, reverse code generating means at the entrance end of said section for supplying reverse code impulses of alternating current energy to the rails of said section at a rate less than the lowest of said trafi'ic code rates, said reverse code generating means including a first and a second impulse relay, said impulse relays alternately governing energization of each other to opcrate in a cyclic manner, means including a contact of said code following track relay for synchronizing the operation of said impulse relays with the reception of code pulses received from the exit end of said section, detector means at the exit end of said section responsive only to said reverse code impulses, said supply means being governed by said detector means to cut off the supply of alternating current energy at the exit end of said section when said reverse code pulses are cut off and the section next in advance is occupied.

4. In a coded signaling system having a code following relay operated at times by impulses of coded energy supplied thereto over a pair of conductors and having a code detecting relay which has its contacts picked up only when said code following relay is recurrently operating its contacts, reverse code generating means for supplying impulses of reverse code energy to said conductors during intervals spaced substantially longer than the intervals between impulses of coded energy received over said con- 'ductors, comprising a first impulse relay and a second impulse relay, said second impulse relay having contacts which are relatively slowing in picking up after the relay is energized, first circuit means governed by said first impulse relay for energizing said second impulse relay when said first impulse relay is released, second circuit means governed by said second impulse relay for energizing said I r 1d V r V first impulse relay when said second'impulse relay is picked up and said code detecting relay is released and for energizing said first impulse relay when said second impulse relay is picked up, said code followingrelay is released, and said code detecting relay is picked up, and means for maintaining said first impulse relay energized for applying a reverse code pulse to said pair of conductors only when said code detecting relay is de-energized. 5. In a coded railway signaling system, in combination, a code following track relay having contacts which are recurrently operated at times by energy supplied thereto over the rails of a track section, a code following repeater relay governed by a contact of said code following track relay, a frontcontact repeater relay governed by said code following repeater relay and having contacts which are picked up when said code following track relay is recurrently operating its contacts, a first impulse relay, a second impulse relay having contacts which are relatively slow in picking up after the relay is energized, a circuit for energizing said second impulse relay including a back contact of said first impulse relay, a first pickup circuit for said first impulse relay including a front contact of said front contact repeater relay, a back contact of said code following repeater relay, a front contact of said second impulse relay and a front contact of said code following track relay, a second pickup circuit for said first impulse relay including a back contact of said front contact repeater relay and a front contact of said second impulse relay, a stick circuit for said first impulse relay including a front contact of said front contact repeater relay, a front contact of said code following repeater relay and a front contact of said first impulse relay, and circuit means governed by a back contact of said code following track relay and a front contact of said first impulse relay for supplying energy to the rails of said track section.

6. In a coded railway signaling system, in combination, a code following track relay having contacts which are recurrently operated at times by energy supplied thereto over the rails of a track section, a code following repeater relay governed by a front contact of said code following track relay, a front contact repeater relay governed by said code following repeater relay and having contacts which are picked up when said code following track relay is recurrently operating its contacts, a first impulse relay, a second impulse relay having contacts which are relatively slow in picking up after the relay is energized, a circuit for energizing said second impulse relay including a back contact of said first impulse relay, a first pickup circuit for said first impulse relay including a front contact of said front contact repeater relay, a back contact of said code following repeater relay, a front contact of said second impulse relay and a front contact of said code following track relay, a second pickup circuit for said first impulse relay including a back contact of said front contact repeater relay and a front contact of said second impulse relay, a stick circuit for said first impulse relay including a front contact of said front contact repeater relay, a front contact of said code following repeater relay and a front contact of said first impulse relay; means governed by said first impulse relay for disconnecting said code following track relay from the rails of said section when said first impulse relay is picked up and said code following relay is de-energized, and circuit means governed by a back contact of said code following track relay and a front contact of said first impulse relay for supplying energy to the rails of said track section only when said code following track relay is de-energized.

7. In a coded railway signaling system,'in combination, a code following track relay having contacts which are recurrently operated at times by energy supplied thereto over the rails of a track section, a front contact repeater relay governed by said codefollowing track relay and having contacts which are picked up when said code following track relay is recurrently operating its-contacts, a first impulse relay, a capacitor, and a source of charging energy for said capacitor; a second impulse relay having contacts which are relatively slow in picking up after a the relay is energized, a circuit (for energizing said second impulse relay including a back contact of said first impulse relay, a first pickup circuit for said first impulse relay including a front contact of said second impulse relay, a back contact of said front contact repeater relay and a back contact of said code following track relay, a second pickup circuit for said first impulse relay including a front contact of said second impulse relay, a back contact of said code following track relay, a front contact of said front contact repeater relay, and said capacitor; a circuit for supplying energy from said source to said capacitor including a front contact of said code following track relay and a front contact of said front contact repeater relay, and means governed by contacts of said first impulse relay for disconnecting said code following relay from the rails of said section when said code following relay is de-energized and for connecting a source of energy to the rails of said section when said first impulse relay is picked up.

20 8. In a coded signaling system having a code following relay operated at times by impulses of coded energy supplied thereto over a pair of conductors, reverse code generating means for supplying impulses of reverse code energy to said pair of conductors when said code following track relay is tie-energized, comprising a first and a second impulse relay, a first circuit means governed by said first impulse relay for energizing said second impulse relay when said first impulse relay is released, second circuit means governed by said second impulse relay for energizing said first impulse relay when said second impulse relay is picked up, holding means for maintaining said first impulse relay energized during an energized period of said code following track relay and until said code following track relay is de-energized, and means governed by a contact of said first impulse relay and a contact of said code following track relay for supplying energy to said pair of conductors.

References Cited in the file of this patent UNITED STATES PATENTS 

